Electric motor or generator

ABSTRACT

An electric motor or generator having a stator having two coil sets arranged to produce a magnetic field for generating a drive torque; two control devices; and a first capacitor arranged to be coupled to a power source for providing current to the two control devices, wherein the first control device is coupled to a first coil set and the first capacitor and the second control device is coupled to a second coil set and the first capacitor, wherein each control device is arranged to control current in the respective coil set to generate a magnetic field in the respective coil set.

The present invention relates to an electric motor or generator, inparticular an electric motor or generator having a capacitor.

Electric motor systems typically include an electric motor and a controlunit arranged to control the power of the electric motor. Examples ofknown types of electric motor include the induction motor, synchronousbrushless permanent magnet motor, switched reluctance motor and linearmotor. In the commercial arena three phase electric motors are the mostcommon kind of electric motor available.

A three phase electric motor typically includes three coil sets, whereeach coil set is arranged to generate a magnetic field associated withone of the three phases of an alternating voltage.

To increase the number of magnetic poles formed within an electricmotor, each coil set will typically have a number of coil sub-sets thatare distributed around the periphery of the electric motor, which aredriven to produce a rotating magnetic field.

By way of illustration, FIG. 1 shows a typical three phase electricmotor 10 having three coil sets 14, 16, 18. Each coil set consists offour coil sub-sets that are connected in series, where for a given coilset the magnetic field generated by the respective coil sub-sets willhave a common phase.

The three coil sets of a three phase electric motor are typicallyconfigured in either a delta or wye configuration.

A control unit for a three phase electric motor having a DC power supplywill typically include a three phase bridge inverter that generates athree phase voltage supply for driving the electric motor. Each of therespective voltage phases is applied to a respective coil set of theelectric motor.

A three phase bridge inverter includes a number of switching devices,for example power electronic switches such as Insulated Gate BipolarTransistor (IGBT) switches, which are used to generate an alternatingvoltage from a DC voltage supply.

To reduce the effects of inductance on inverters when switching current,capacitors are used as a local voltage source for electric motorinverters. By placing a capacitor close to an inverter the inductanceassociated with the voltage source is minimised.

Accordingly, where there is a need for reduced inductance, typically anelectric motor that comprises a plurality of sub-motors each with arespective inverter will have separate capacitors associated with eachinverter, where the additional capacitors result in an increased spaceenvelope requirement and increase in cost, with a potential reduction inreliability.

It is desirable to improve this situation

In accordance with an aspect of the present invention there is providedan electric motor or generator according to the accompanying claims.

As a result of a plurality of inverters drawing different amounts ofcurrent at any given time, by using a single capacitor to support theplurality of inverters the present invention provides the advantage ofreducing the overall capacitance requirements for an electric motor witha corresponding reduction in space. Additionally a single annularcapacitor allows the capacitor to be mounted close to the plurality ofseparate inverters, thereby reducing inductive effects and removing theneed for snubber capacitors.

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 illustrates a prior art three phase electric motor;

FIG. 2 illustrates an exploded view of a motor embodying the presentinvention;

FIG. 3 illustrates an exploded view of the electric motor shown in FIG.1 from an alternative angle;

FIG. 4 illustrates an electric motor according to an embodiment of thepresent invention;

FIG. 5 illustrates control modules for an electric motor according to anembodiment of the present invention;

FIG. 6 illustrates a partial view for an electric motor according to anembodiment of the present invention;

FIG. 7 illustrates a control module for an electric motor according toan embodiment of the present invention;

FIG. 8 illustrates a cross sectional view of a stator according to anembodiment of the present invention;

FIG. 9 illustrates a capacitor element according to an embodiment of thepresent invention;

FIG. 10 illustrates a schematic diagram for a capacitor according to anembodiment of the present invention;

FIG. 11 illustrates a cross sectional view of a capacitor according toan embodiment of the present invention;

FIG. 12 illustrates a capacitor element according to an embodiment ofthe present invention;

FIG. 13 illustrates a capacitor element according to an embodiment ofthe present invention;

FIG. 14 illustrates a capacitor element according to an embodiment ofthe present invention;

FIG. 15 illustrates a capacitor element according to an embodiment ofthe present invention;

FIG. 16 illustrates a partial view of a control module housing accordingto an embodiment of the present invention.

The embodiment of the invention described is for an electric motorhaving a capacitor element, where the electric motor is for use in awheel of a vehicle. However the electric motor may be located anywherewithin the vehicle. The motor is of the type having a set of coils beingpart of the stator for attachment to a vehicle, radially surrounded by arotor carrying a set of magnets for attachment to a wheel. For theavoidance of doubt, the various aspects of the invention are equallyapplicable to an electric generator having the same arrangement. Assuch, the definition of electric motor is intended to include electricgenerator. In addition, some of the aspects of the invention areapplicable to an arrangement having the rotor centrally mounted withinradially surrounding coils. As would be appreciated by a person skilledin the art, the present invention is applicable for use with other typesof electric motors.

For the purposes of the present embodiment, as illustrated in FIG. 2 andFIG. 3, the in-wheel electric motor includes a stator 252 comprising aheat sink 253, multiple coils 254, two control modules 400 mounted onthe heat sink 253 on a rear portion of the stator for driving the coils,and a capacitor (not shown) mounted on the stator within a recess 255formed on the rear portion of the stator. In a preferred embodiment thecapacitor is an annular capacitor element. The coils 254 are formed onstator tooth laminations to form coil windings, where the stator toothlaminations are mounted on the heat sink 253. The heat sink 253 includesat least one cooling channel for allowing a coolant to flow within theheat sink 253 for providing cooling, thereby allowing the heat sink 253to extract heat from components attached to the heat sink 253, forexample the coil windings and the control modules. A stator cover 256 ismounted on the rear portion of the stator 252, enclosing the controlmodules 400 to form the stator 252, which may then be fixed to a vehicleand does not rotate relative to the vehicle during use.

Each control module 400 includes two inverters 410 and control logic420, which in the present embodiment includes a processor, forcontrolling the operation of the inverters 410, which is schematicallyrepresented in FIG. 5.

The annular capacitor element is coupled across the inverters 410 fordistributing the DC power supply to the inverters 410 and for reducingvoltage ripple on the electric motor's power supply line, otherwiseknown as the DC busbar, during operation of the electric motor, asdescribed below. For reduced inductance the annular capacitor element ismounted adjacent to the control modules 400. Although the capacitorelement within the electric motor of the present embodiment is anannular capacitor, the capacitor element may be of any shape.

A rotor 240 comprises a front portion 220 and a cylindrical portion 221forming a cover, which substantially surrounds the stator 252. The rotorincludes a plurality of permanent magnets 242 arranged around the insideof the cylindrical portion 221. For the purposes of the presentembodiment 32 magnet pairs are mounted on the inside of the cylindricalportion 221. However, any number of magnet pairs may be used.

The magnets are in close proximity to the coil windings on the stator252 so that magnetic fields generated by the coils interact with themagnets 242 arranged around the inside of the cylindrical portion 221 ofthe rotor 240 to cause the rotor 240 to rotate. As the permanent magnets242 are utilized to generate a drive torque for driving the electricmotor, the permanent magnets are typically called drive magnets.

The rotor 240 is attached to the stator 252 by a bearing block 223. Thebearing block 223 can be a standard bearing block as would be used in avehicle to which this motor assembly is to be fitted. The bearing blockcomprises two parts, a first part fixed to the stator and a second partfixed to the rotor. The bearing block is fixed to a central portion 253of the wall of the stator 252 and also to a central portion 225 of thehousing wall 220 of the rotor 240. The rotor 240 is thus rotationallyfixed to the vehicle with which it is to be used via the bearing block223 at the central portion 225 of the rotor 240. This has an advantagein that a wheel rim and tyre can then be fixed to the rotor 240 at thecentral portion 225 using the normal wheel bolts to fix the wheel rim tothe central portion of the rotor and consequently firmly onto therotatable side of the bearing block 223. The wheel bolts may be fittedthrough the central portion 225 of the rotor through into the bearingblock itself. With both the rotor 240 and the wheel being mounted to thebearing block 223 there is a one to one correspondence between the angleof rotation of the rotor and the wheel.

FIG. 3 shows an exploded view of the same motor assembly illustrated inFIG. 2 from the opposite side. The rotor 240 comprises the outer rotorwall 220 and circumferential wall 221 within which magnets 242 arecircumferentially arranged. As previously described, the stator 252 isconnected to the rotor 240 via the bearing block at the central portionsof the rotor and stator walls.

A V shaped seal is provided between the circumferential wall 221 of therotor and the outer edge of the stator.

The rotor also includes a set of magnets 227 for position sensing,otherwise known as commutation magnets, which in conjunction withsensors mounted on the stator allows for a rotor flux angle to beestimated. The rotor flux angle defines the positional relationship ofthe drive magnets to the coil windings. Alternatively, in place of a setof separate magnets the rotor may include a ring of magnetic materialthat has multiple poles that act as a set of separate magnets.

To allow the commutation magnets to be used to calculate a rotor fluxangle, preferably each drive magnet has an associated commutationmagnet, where the rotor flux angle is derived from the flux angleassociated with the set of commutation magnets by calibrating themeasured commutation magnet flux angle. To simplify the correlationbetween the commutation magnet flux angle and the rotor flux angle,preferably the set of commutation magnets has the same number of magnetsor magnet pole pairs as the set of drive magnet pairs, where thecommutation magnets and associated drive magnets are approximatelyradially aligned with each other. Accordingly, for the purposes of thepresent embodiment the set of commutation magnets has 32 magnet pairs,where each magnet pair is approximately radially aligned with arespective drive magnet pair.

A sensor, which in this embodiment is a Hall sensor, is mounted on thestator. The sensor is positioned so that as the rotor rotates each ofthe commutation magnets that form the commutation magnet ringrespectively rotates past the sensor.

As the rotor rotates relative to the stator the commutation magnetscorrespondingly rotate past the sensor with the Hall sensor outputtingan AC voltage signal, where the sensor outputs a complete voltage cycleof 360 electrical degrees for each magnet pair that passes the sensor.

For improved position detection, preferably the sensor includes anassociated second sensor placed 90 electrical degrees displaced from thefirst sensor.

As illustrated in FIG. 4, in the present embodiment the electric motorincludes four coil sets 60 with each coil set 60 having three coilsub-sets 61, 62, 63 that are coupled in a wye configuration to form athree phase sub-motor, resulting in the motor having four three phasesub-motors. The operation of the respective sub-motors is controlled viaone of two control devices/control modules 400, as described below.However, although the present embodiment describes an electric motorhaving four coil sets 60 (i.e. four sub motors) the motor may equallyhave one or more coil sets with associated control devices. In apreferred embodiment the motor 40 includes eight coil sets 60 with eachcoil set 60 having three coil sub-sets 61, 62, 63 that are coupled in awye configuration to form a three phase sub-motor, resulting in themotor having eight three phase sub-motors. Similarly, each coil set mayhave any number of coil sub-sets, thereby allowing each sub-motor tohave two or more phases.

FIG. 5 illustrates the connections between the respective coil sets 60and the control modules 400, where a respective coil set 60 is connectedto a respective three phase inverter 410 included in a control module400. As is well known to a person skilled in the art, a three phaseinverter contains six switches, where a three phase alternating voltagemay be generated by the controlled operation of the six switches.However, the number of switches will depend upon the number of voltagephases to be applied to the respective sub motors, where the sub motorscan be constructed to have any number of phases.

The respective coils of the four coil sets are wound on individualstator teeth, which form part of the stator. The end portions 501 of thecoil windings protrude through the planar rear portion 502 of the statorheat sink, as illustrated in FIG. 6. FIG. 6 illustrates a partialperspective view of the stator, where the end portions 501 of the coilwindings for two of the four coil sets 60 extend away from the planarportion of the stator heat sink 253.

The control modules 400 are positioned adjacent to the planar portion ofthe stator heat sink 253, for mounting to the planar portion of thestator heat sink 253. For illustration purposes, a view of a singlecontrol module 400 separated from the stator heat sink 253 is shown inFIG. 6. As stated above, an annular recess 255 is formed in the planarportion of the heat sink 253 for housing the annular capacitor element.

For the purposes of the present embodiment, the planar portion of theheat sink 253 is located on the side of the stator that is intended tobe mounted to a vehicle.

Preferably, to facilitate the mounting of the respective control modules400 to the stator heat sink 253, the end sections 501 of the coilwindings for the respective coil sets are arranged to extend away fromthe heat sink portion of the stator in a substantially perpendiculardirection relative to the surface of the heat sink portion of thestator.

FIG. 7 illustrates a modular construction of the control module 400 withan exploded view of a preferred embodiment of a control module 400,where each control module 400, otherwise known as a power module,includes a power printed circuit board 500 in which are mounted twopower substrate assemblies 510, a control printed circuit board 520,four power source busbars (not shown) for connecting to the annularcapacitor element, six phase winding busbars (not shown) for connectingto respective coil windings, two insert modules 560 and six currentsensors. Each current sensor includes a Hall sensor and a section ofsoft ferromagnetic material 530 arranged to be mounted adjacent to theHall sensor, where preferably each Hall sensor is arranged to be mountedin a cutout section of a piece of soft ferromagnetic material fashionedin a toroid shape.

Each of the control module components are mounted within a controlmodule housing 550 with the four power source busbars and the six phasewinding busbars being mounted, via the respective insert modules, on thepower printed circuit board 500 on opposite sides of the control devicehousing 550.

Each power substrate 510 is arranged to be mounted in a respectiveaperture formed in the power printed circuit board 500, where each ofthe power substrates 510 has a 3 mm copper base plate 600 upon which isformed a three phase inverter 410. A corresponding aperture 511 is alsoformed in the control module housing 550 to allow the copper base platefor each of the power substrates 510 is placed in direct contact withthe stator heat sink 253 when the control device housing 550 is mountedto the stator, thereby allowing for cooling to be applied directly tothe base of each of the power substrates 510.

Mounted on the underside of the power printed circuit board 500,adjacent to the copper base plate of the power substrate assemblies 510,are the six Hall sensors (not shown) for measuring the current in therespective coil windings associated with two of the four coil sets. TheHall sensor readings are provided to the control printed circuit board520.

The power printed circuit board 500 includes a variety of othercomponents that include drivers for the inverter switches formed on thepower substrate assemblies 510, where the drivers are used to convertcontrol signals from the control printed circuit board 520 into asuitable form for operating switches mounted on the power printedcircuit board 500, however these components will not be discussed in anyfurther detail.

The insert modules 560 are arranged to be mounted over the power printedcircuit board 500 when the power printed circuit board 500 is mounted inthe control module housing 550.

Each insert module 560 is arranged to be mounted over a respective powersubstrate assembly 510 mounted on the power printed circuit board 500,with each insert module 560 having an aperture arranged to extend aroundinverter switches formed on a respective power substrate assembly 510.

Each insert module 560 is arranged to carry two power source busbars andthree phase windings busbars for coupling the inverter formed on thepower substrate assembly 510, over which the insert module 560 ismounted, to the annular capacitor element and to the phase windings of acoil set, respectively.

The insert module 560 also acts as a spacer for separating the controlprinted circuit board 520 from the power printed circuit board 500 whenboth the power printed circuit board 500 and the control printed circuitboard 520 are mounted in the control module housing 550.

A first pair of the power source busbars mounted on one of the insertmodules 560 is for providing a voltage source to a first inverter 410formed on one of the power substrates assemblies 510. A second pair ofthe power source busbars mounted on a second insert module 560 is forproviding a voltage source to a second inverter 410 formed on the otherpower substrate assembly 510.

For each pair of power source busbars, one of the power source busbarsis located in a first plane formed above the plane of the power circuitboard 500. The other power source busbar is located in a second planeabove the first plane. Preferably, each pair of power source busbars arearranged to be substantially co-planar.

Located in the control module housing 550 on the opposite side of therespective power substrate assemblies 510 to the power source busbarsare the six phase winding busbars. A phase winding busbar is coupled toeach inverter leg for coupling to a respective coil winding, as is wellknown to a person skilled in the art (i.e. a phase winding busbar iscoupled to each leg of the three phase inverter formed on one of thepower substrate assemblies 510 and a phase winding busbar is coupled toeach leg of the three phase inverter formed on the other power substrateassembly 510).

The control printed circuit board 520 is arranged to be mounted in thecontrol module housing 550 above the power printed circuit board 500.

The control printed circuit board 520 includes a processor 420 forcontrolling the operation of the respective inverter switches to alloweach of the electric motor coil sets 60 to be supplied with a threephase voltage supply using PWM voltage control across the respectivecoil sub-sets 61, 62, 63. For a given torque requirement, the threephase voltage applied across the respective coil sets is determinedusing field oriented control FOC, which is performed by the processor onthe control printed circuit board using the current sensors mountedwithin the control module housing 550 for measuring the generatedcurrent.

PWM control works by using the motor inductance to average out anapplied pulse voltage to drive the required current into the motorcoils. Using PWM control an applied voltage is switched across the motorwindings. During the period when voltage is switched across the motorcoils, the current rises in the motor coils at a rate dictated by theirinductance and the applied voltage. The PWM voltage control is switchedoff before the current has increased beyond a required value, therebyallowing precise control of the current to be achieved.

The inverter switches can include semiconductor devices such as MOSFETsor IGBTs. In the present example, the switches comprise IGBTs. However,any suitable known switching circuit can be employed for controlling thecurrent. One well known example of such a switching circuit is the threephase bridge circuit having six switches configured to drive a threephase electric motor. The six switches are configured as three parallelsets of two switches, where each pair of switches is placed in seriesand form a leg of the three phase bridge circuit. A DC power source iscoupled across the legs of the inverter, with the respective coilwindings of an electric motor being coupled between a respective pair ofswitches, as is well known to a person skilled in the art. A singlephase inverter will have two pairs of switches arranged in series toform two legs of an inverter.

The three phase voltage supply results in the generation of current flowin the respective coil sub-sets and a corresponding rotating magneticfield for providing a required torque by the respective sub-motors.

Additionally, each control printed circuit board 520 includes aninterface arrangement to allow communication between the respectivecontrol modules 400 via a communication bus with one control module 400being arranged to communicate with a vehicle controller mounted externalto the electric motor, where the externally mounted controller willtypically provide a required torque value to the control module 400. Theprocessor 420 on each control modules 400 is arranged to handlecommunication over the interface arrangement.

As stated above, although the present embodiment describes each coil set60 as having three coil sub-sets 61, 62, 63, the present invention isnot limited by this and it would be appreciated that each coil set 60may have one or more coil sub-sets.

FIG. 8 illustrates a cross sectional view of a section of the statorwith the annular capacitor element 800 being housed within a capacitorelement housing 810 mounted within the annular recess 255 formed in theplanar portion of the heat sink 253.

The annular capacitor element 800 includes a first busbar, where thefirst busbar is coupled to a first internal capacitor electrode via afirst external electrode. A second busbar mounted adjacent to the firstbusbar is coupled to a second internal capacitor electrode via a secondexternal electrode, as described below. The first busbar allows chargeto flow to and from the first internal capacitor electrode. The secondbusbar allows charge to flow to and from the second internal capacitorelectrode. The first internal capacitor electrode and the secondinternal capacitor electrode correspond to the capacitor plates.

FIG. 9 illustrates an exploded view of the annular capacitor element800, where both the first busbar 900 and the second busbar 910 aremounted around the outer circumferential surface of an annular capacitorcomponent 920 with the first busbar 900 and the second busbar 910 beingseparated by a first insulating film 930. The first busbar 900 iselectrically isolated from the outer circumference of the annularcapacitor component 920 with a second insulating film 940.

Having concentric busbars 900, 910 formed around the annular capacitorcomponent, where the busbars 900, 910 are separated by a thin insulationlayer 930, rather than being placed on separate sides of a capacitorelement, minimises the inductance, thereby reducing losses in theinverter.

The first busbar 900 includes a first electrical coupling element 950for coupling the first busbar 900 to a first terminal of a DC powersource, for example a battery located within the vehicle housing thein-wheel electric motor. Similarly, the second busbar 910 includes asecond electrical coupling element 960 for coupling the second busbar toa second terminal of the DC power source, thereby allowing the annularcapacitor element to be coupled in parallel between the DC power sourceand the respective inverters mounted in the in-wheel electric motor.

Additionally, the first busbar and the second busbar include couplingmembers 980 for coupling to the respective inverter power source busbarsmounted in the control modules to allow the annular capacitor element800 to act as a voltage source to each of the corresponding inverters,thereby allowing a single capacitor to be used to support a plurality ofinverters.

In one embodiment, the first busbar 900 and the second busbar 910 may beprefabricated annular components that are push fit onto the annularcapacitor component 920 so that the busbars 900, 910 are concentric.However, to minimise the dimensional tolerances of the busbars 900, 910and the risk of damage to the capacitor assembly that could result fromthermal expansion, preferably at least one of the busbars 900, 910 aremanufactured as C shapes, where a section 970 of each of the busbars900, 910 is removed to allow for variations in the diameter of theannular capacitor component 920 resulting from manufacture and/orthermal expansion. Similarly, having a gap in the first busbar 900 andthe second busbar 910 allows the busbars to expand/contract withoutcausing stress to the surrounding components. The gap that is formed inthe first busbar 900 and the second busbar 910 to form the C shapedbusbars may be of any suitable size, however preferably the size of thegap will calculated using the coefficient of thermal expansion values ofthe materials used for the busbars and engineering manufacturingtolerances and component size to determine a gap size that will avoidthe ends of the busbars coming into contact over the thermal envelope ofthe electric motor.

As described below, preferably the annular capacitor component 920combines a plurality of capacitors into a single capacitor element,where the annular capacitor component 920 includes a first capacitor, asecond capacitor and a third capacitor.

The first capacitor is arranged to couple the DC voltage source to therespective inverters mounted in the control modules 400 on the electricmotor, where the first capacitor is arranged to inhibit voltagetransients generated across the inverter switches, which could causelosses and electrical stress on the switching devices and provide highpulse current loads from the inverter. This has the effect of reducinginductance on the inverters during current switching. The firstcapacitor element is coupled in parallel between the DC voltage sourceand the respective inverters.

To reduce electro-magnetic noise generated by the inverters, the annularcapacitor component 920 also includes integrated second and thirdcapacitors that are connected in line with the first capacitor. Thesecond and third capacitors act as Y capacitor elements and are coupledin series with each other and in parallel with the first capacitor.Although the second and third capacitors are integrated with the firstcapacitor to form an annular capacitor element, the second and thirdcapacitors may also be formed as separate elements to the firstcapacitor.

Y capacitors act as part of an EMC solution within an electric motorsystem, where Y capacitors are used in combination with a local DC linkcapacitor (i.e. the first capacitor) to reduce/control electromagneticemissions by providing a path for common mode EMC currents to flow backto the DC link, thereby reducing the EMC currents flowing out of themotor.

For an electric motor having a plurality of sub-motors with associatedinverters, typically two Y capacitors are required for each inverter.For a multi-inverter configuration this can have an adverse impact onpackaging, cost and reliability of an electric motor system. However,the present invention allows a single Y capacitor configuration tosupport multiple inverters, thereby reducing packaging requirements andsimplifying the manufacturing process.

FIG. 10 illustrates an equivalent circuit for the integrated annularcapacitor component 920 with the first capacitor 1010 being coupledbetween the positive and negative power rails of the DC voltage sourcewith the second capacitor 1020 being coupled between the positive powerrail and a reference potential, for example the vehicle chassis, and thethird capacitor 1030 being coupled between the negative power rail andthe reference potential. As stated above, the respective inverters arecoupled across the positive and negative power rails of the DC voltagesource.

By using a single capacitor to support a plurality of inverters theoverall capacitance can be reduced, with a reduction in space, as theplurality of inverters will not draw the same current at the same timedue to switching, timing and inverter demand variations. A singlecapacitor can be configured to be close to the plurality of separateinverters when configured as an annular element, thereby reducinginductive effects and removing the need for snubber capacitors.

FIG. 11 illustrates a cross sectional view of one section of the annularcapacitor element 800, including the first busbar 900 and the secondbusbar 910.

The annular capacitor component 920 includes at least one dielectricfilm wound to form an annular element, where a plurality of internalelectrodes (i.e. the capacitor plates) is formed on the film. Theinternal electrodes may be formed by any suitable means, however for thepurposes of the present embodiment the internal electrodes are formed bycreating a metallization layer on the film. In an alternative embodimenta plurality of films may be used with a separate electrode formed oneach film. For example, two layers of film each with a metal coatingformed on one side of the respective films, which are wrapped round in acylindrical shape.

To simplify the connections between the respective capacitors that formthe annular capacitor component 920, for the purposes of the presentembodiment the third capacitor is integrated between the first capacitorand the second capacitor. However, the capacitors can be arranged in anyorder.

The first capacitor 1010, second capacitor 1020 and third capacitor 1030may be formed using a single film with an insulating region formed onthe film to electrically separate the first capacitor 1010 from thethird capacitor 1030 and an insulating region formed on the film toelectrically separate the third capacitor 1030 from the second capacitor1020 (e.g. the metal coating is removed from a portion of the film).However, for the purposes of the present embodiment the first capacitor1010, the second capacitor 1020 and the third capacitor 1030 are formedon separate films, where the film for the third capacitor 1030 is woundon the first capacitor 1010 and the film for the second capacitor 1020is wound on the third capacitor 1030 to form a capacitor element havingthree separate film layers with each separate film layer correspondingto a separate capacitor. For increased electrical isolation between thecapacitor elements, preferably a separate insulating film is placedbetween the first capacitor 1010 and the third capacitor 1030 andbetween the third capacitor 1030 and the second capacitor 1020.

The dielectric film may be made from any suitable material, for examplea polymer film.

The metallization layers formed on the dielectric films that form theinternal electrodes of the first capacitor 1010, the second capacitor1020 and the third capacitor 1030 are arranged to extend to one edge ofthe dielectric film that is normal to the surface of the film. Inparticular, a first metallization layer, which forms a first electrode,is arranged to extend to one edge of the dielectric film that is normalto the surface of the film. However, the first metallization layer doesnot extend to the opposite edge of the dielectric film, thereby leavingan insulated region on the opposite edge of the dielectric film. Thecorresponding second metallization layer, which forms a secondelectrode, is arranged to extend to the edge of the dielectric film thatis normal to the surface of the film and that is opposite to the edgethat the first metallization layer is arranged to extend to. The secondmetallization layer does not extend to the opposite edge of thedielectric film, thereby leaving an insulated region on the oppositeedge of the dielectric film.

Consequently, the edges of the metallization layers are used as thepositive and negative plates of the capacitor elements, where the edgesof the annular capacitor element that are normal to the surface of thedielectric film are covered by a metal layer to form a first externalelectrode 1110 and a second external electrode 1120 respectively for theannular capacitor element.

Having a multi-element capacitor with integrated capacitor elements itis necessary that the individual capacitor elements be capable of beingisolated from each other to enable specific electrical connections to bemade to the respective capacitor terminals.

To achieve electrical isolation between the respective capacitorelements the first external electrode 1110 is divided into two sections,where an insulation layer 1130 divides the first external electrode 1110at the interface between the first capacitor 1010 and the thirdcapacitor 1030. The insulation layer 1130 takes the form of a firstisolation film that is placed between the first capacitor 1010 and thethird capacitor 1030 to provide an insulation barrier between the twosections of the first external electrode 1110 to form a radially innersection 1140 and a radially outer section 1150. Preferably, the existinginsulating film used within the film capacitor may be used to form thisinsulation barrier. For improved electrical isolation between the innerradial section 1140 and the outer radial section 1150 of the firstexternal electrode 1110 the first isolation film 1130 is arranged toextend perpendicular away from the surface of the first externalelectrode 1110, that is to say the insulation film 1130 protrudes abovethe terminal surface extending the clearance distance, as illustrated inFIG. 11.

The second external electrode 1120 is divided into two sections, wherean insulation layer 1160 divides the second external electrode 1120, atthe interface between the second capacitor 1020 and the third capacitor1030. The insulation layer 1160 takes the form of a second isolationfilm that is placed between the second capacitor 1020 and the thirdcapacitor 1030 to provide an insulation barrier between the two sectionsof the second external electrode 1120 to form a radially inner section1170 and a radially outer section 1180. Preferably, the existinginsulating film used within the film capacitor may be used to form aninsulation barrier. For improved electrical isolation between the innerradial section 1170 and the outer radial section 1180 of the secondexternal electrode 1120 the second isolation film 1160 is arranged toextend perpendicularly away from the surface of the second externalelectrode 1120, that is to say the insulation film 1160 protrudes abovethe terminal surface extending the clearance distance, as illustrated inFIG. 11.

By allowing the respective insulation films 1130, 1160 to extend awayfrom the surfaces of the external electrodes 1110, 1120, this allows thebusbar connection points to the external electrodes 1110, 1120 of thecapacitor element to be placed near to the interface/junction betweencapacitor elements so that size/width of the annular capacitor element800 does not need to be increased.

As stated above, mounted around the outer circumferential surface of theannular capacitor component are the first busbar 900 and the secondbusbar 910, where the first busbar 900 and the second busbar 910 areelectrically isolated from each other using an insulation film placedbetween them.

In the present embodiment, the internal electrodes for the firstcapacitor 1010, the second capacitor 1020 and the third capacitor 1030and the first and second busbars 900, 910 are radially symmetricalaround an axis.

To allow electrical connections to be made between the first externalcapacitor electrode 1110, the second external capacitor electrode 1120,the first busbar 900 and the second busbar 910; the first busbar 900 andthe second busbar 910 include contact arms for making electrical contactwith the first external capacitor electrode 1110 and the second externalcapacitor electrode 1120. A contact arm 1210 for the first busbar 900 isillustrated in FIG. 12.

The busbar contact arms extend from the main body of the respectivebusbars 900, 910 in a direction towards the annular capacitor componentat substantially 90 degrees to the internal capacitor electrodes. Thisorientation of the busbar contact arms 1210 allows the busbar contactarms to extend over the respective external capacitor electrodes.

FIG. 11 illustrates the respective electrical connections between thefirst busbar and the second busbar to the respective capacitors thatform the annular capacitor element to provide the equivalent circuitillustrated in FIG. 10.

A first contact arm 1190 formed on one end of the first busbar 900 iscoupled to the inner radial portion 1140 of the first external capacitorelectrode 1110 with a second contact arm 1191 formed on the opposite endof the first busbar 900 being coupled to the outer radial portion 1180of the second external capacitor electrode 1120. The first contact arm1190 is arranged to extend over the insulation film 1130 protruding frombetween the first capacitor 1010 and the third capacitor 1030.

A second contact arm 1192 formed on one end of the second busbar 910 iscoupled to the inner radial portion 1170 of the second externalcapacitor electrode 1120. The second contact arm 1192 is arranged toextend over the insulation film 1160 protruding from between the thirdcapacitor 1030 and the second capacitor 1020.

The outer radial portion 1150 of the first external capacitor electrode1110 is arranged to be coupled to a reference potential, for example thevehicle chassis.

To minimise the manufacturing cost of the respective busbars 900, 910,the busbars 900, 910 are arranged to have multiple sections ofsubstantially identical contact arms for electrically coupling thebusbars 900, 910 to the annular capacitor component 920 and power sourcecoupling members 980 for coupling the busbars 900, 910 to the invertershoused in the respective control modules 400. The multiple sections forma repeating pattern that allows smaller/cheaper tooling to cut outsections of the capacitor busbar repeatedly rather than using a singlelarge tool in a one shot process. The multiple repeating pattern isillustrated in FIG. 12 and FIG. 13.

Additionally, by placing the first busbar 900 and the second busbar 910around the outer circumference of the annular capacitor component 920,otherwise known as the capacitor ring, in parallel with the firstinternal capacitor electrode and the second internal capacitor electrodeand perpendicular to the first external capacitor electrode 1110 and thesecond external capacitor electrode 1120 increases the surface area ofthe capacitor busbars, thereby allowing the thickness of the metalsheets that make up the first busbar 900 and the second busbar 910 to bereduced. This ensures that the axial width of the capacitor ring doesnot increase while having minimum impact on the diameter of thecapacitor ring. Increased surface area of the busbar also results inreduced inductance and temperature of the busbar. Additionally, byincreasing the surface area of the busbar allows the cross-sectionalthickness of the metal sheets used to manufacture the busbars to bereduced, thereby allowing the metal sheets that make up the busbars tobe more easily rolled around the annular capacitor element for ease ofmanufacturing of the component.

FIG. 14 illustrates a perspective view of the annular capacitor element800 mounted within an annular capacitor element housing 810 and anexploded view of the annular capacitor element 800 and the annularcapacitor element housing 810.

FIG. 15 illustrates a plan view and a cross sectional view of theannular capacitor component 920.

To allow the respective coil windings for two of the four coil sets 60to be coupled to a respective phase winding busbar within a controlmodule housing 550, the control module housing 550 is arranged to havesix apertures 610.

The six apertures 610 are formed on an outer edge of the control modulehousing 550 on the side of the housing 550 that is to be mountedadjacent to the planar portion of the stator heat sink 253.

The size and position of the six apertures 610 formed in the controlmodule housing 550 are arranged to match the positions and diameters ofthe end portions of the coil windings that extend from the planarportion of the stator heat sink 253, thereby allowing the respective endportions of the coil windings to extend through the apertures 610 whenthe control housing module 550 is mounted on to the planar portion ofthe stator heat sink 253.

A partial perspective view of the control module housing 550 isillustrated in FIG. 16. A recess 710 is formed around each of the sixapertures 610 formed in the control module housing 550, where eachrecess 710 is sized to allow a partial toroid made of soft ferromagneticmaterial 530, for example a ferrite element, to be located in the recess710. The top of the partial toroid is arranged to be substantially levelwith the bottom section of the control module housing 550 when thepartial toroid 530 is mounted in a recess 710. The partial toroid offerromagnetic material 530 has a section missing from the toroid thatsubstantially corresponds to the size of the Hall sensor mounted on thepower printed circuit board 500. To facilitate the guiding of the coilwindings as they pass through the aperture 610, the control modulehousing 550 is arranged to have a conduit section formed around eachaperture 610. The conduit sections formed around each of the respectiveapertures also prevent an elastomer placed in the control module housing550 from escaping through the apertures during the curing process forthe elastomer.

Preferably the recesses 710 formed in the base of the control modulehousing 550 are keyed to ensure that the partial toroids of softferromagnetic material 530 can only be oriented within a recess 710 in aposition where the missing section of the toroid is aligned with theposition of the Hall sensor mounted on the power printed circuit board500 when the power printed circuit board 500 is mounted within thecontrol module housing 550.

Once the partial toroids of soft ferromagnetic material 530 have beenmounted in the respective recesses 710 formed in the base of the controlmodule housing 550, the power printed circuit board 500 is lowered intoposition in the control module housing. Upon the power printed circuitboard 500 being lowered into position in the control module housing 550,as a result of the alignment of the partial toroids of softferromagnetic material 530 and the Hall sensors mounted on the powerprinted circuit board 500, the Hall sensors mounted on the power printedcircuit board 500 are inserted into the missing sections of therespective partial toroids 530 mounted in the control module housing550.

Once the power printed circuit board 500 has been lowered into positionin the control module housing the insert modules are positioned over arespective power substrate assembly with the respective inverter formedon the power substrates being coupled to the respective power sourcebusbars and phase winding busbars.

Each of the phase winding busbars formed on the respective insertmodules are arranged to include a coupling section for coupling thephase winding busbar to a phase winding of one of the coil sets. Thecoupling section for each phase winding busbar is arranged to extendaround a respective aperture 610 formed in the base of the controlmodule housing 550.

The control printed circuit board 520 is then mounted in the controlmodule housing 550 above the power printed circuit board 500, with thecontrol printed circuit board 520 being electrically coupled to thepower printed circuit board 500 to allow the control printed circuitboard 520 to control the operation of the switches on the invertersformed on the power substrate assemblies 510.

To mount the control module 400 to the stator, the respective endsections of the coil windings form two coil sets 60 that extend awayfrom the planar surface of the stator heat sink 253 (i.e. six coilwinding end sections) are aligned with the respective apertures 610formed in the base of the control module housing 550. The control module400 is then pushed flush with the surface of the stator so that therespective end sections of the coil windings for two coil sets 60 thatextend away from the planar surface of the stator heat sink 253 (i.e.six coil winding end sections) extend through the respective apertures610 formed in the base of the control module housing 550 with each ofthe current sensors mounted in the control module 400 being mountedadjacent to a respective end section of a coil winding.

The control module may be mounted to the stator by any suitable means,for example one or more bolts that extend through the control moduleinto the surface of the stator heat sink.

Once the control module has been mounted to the stator, the respectivecoupling sections of the phase winding busbars mounted on the powerprinted circuit board 500 are coupled to a respective end section of acoil winding, where any suitable means may be used to couple thecoupling section of the phase winding busbar to a respective end sectionof a coil winding, for example crimping or welding. Similarly, therespective power source busbars housed in the control modules arecoupled to respective coupling members on the first busbar and thesecond busbar using any suitable means, for example crimping or welding.

The inverter 410 formed on one power assembly 510, which is coupled viathe respective phase winding busbars to a first coil set 60, is arrangedto control current in the first coil set. The other inverter 410 formedon the other power assembly 510 in the control module 400 is arranged tocontrol current in a second coil set 60, where the current measurementsmade by the respective current sensors are used by the processor on thecontrol printed circuit board 520 to control current in the respectivecoil sets 60.

Similarly, the second control module 400 is arranged to control currentin a third and fourth coil set 60.

The invention claimed is:
 1. An electric motor or generator comprising astator having two coil sets arranged to produce a magnetic field forgenerating a drive torque; two control devices; and a capacitorcomponent arranged to be coupled to a power source for providing currentto the two control devices, wherein the first control device is coupledto a first coil set and the capacitor component and the second controldevice is coupled to a second coil set and the capacitor component,wherein each control device is arranged to control current in therespective coil set to generate a magnetic field in the respective coilset, wherein the capacitor component includes a first capacitorintegrated with a Y-capacitor, wherein the Y-capacitor includes a secondcapacitor and a third capacitor, wherein the second and the thirdcapacitor are arranged in series with each other and in parallel to thefirst capacitor.
 2. An electric motor or generator according to claim 1,wherein each coil set includes a plurality of coil sub-sets, wherein thefirst control device is coupled to the plurality of coil sub-sets forthe first coil set and the second control device is coupled to theplurality of coil sub-sets for the second coil set and each controldevice is arranged to control current in the respective plurality ofcoil sub-sets to generate a magnetic field in each coil sub-set to havea substantially different magnetic phase to the other one or more coilsub-set in the respective coil set.
 3. An electric motor or generatoraccording to claim 2, wherein the first control device and secondcontrol device are arranged to drive each of the coil sub-sets with adifferent voltage phase.
 4. An electric motor or generator according toclaim 2, wherein the first control device and second control device arearranged to control the voltage to each coil sub-set using pulse widthmodulation.
 5. An electric motor or generator according to claim 1,wherein the first control device, the second control device and thecapacitor component are mounted adjacent to the stator.
 6. An electricmotor or generator according to claim 1, wherein the capacitor componentis in the form of an annular disc.
 7. An electric motor or generatoraccording to claim 1, wherein the stator includes an annular recess forhousing the capacitor component.
 8. An electric motor or generatoraccording to claim 7, wherein the first control device and the secondcontrol device are mounted on the stator adjacent to the annular recess.9. An electric motor or generator according to claim 7, wherein thefirst control device and the second control device are mounted on thestator between the outer radial edge of the stator and the annularrecess.
 10. An electric motor or generator according to claim 1, whereinthe first control device includes a first inverter for controllingcurrent flow in the first coil set and the second control deviceincludes a second inverter for controlling current flow in the secondcoil set, wherein each inverter is coupled to the first capacitor. 11.An electric motor or generator according to claim 10, wherein the firstinverter and the second inverter are mounted at substantially the samedistance radially from the capacitor component.
 12. An electric motor orgenerator according to claim 1, wherein the capacitor component includesa first electrical busbar coupled to a first electrical terminal of thefirst capacitor and a second electrical busbar coupled to a secondelectrical terminal of the first capacitor.
 13. An electric motor orgenerator according to claim 12, wherein the first electrical busbar hasa first contact arrangement for coupling the first inverter to thecapacitor component and a second contact arrangement for coupling thesecond inverter to the capacitor component, wherein the configuration ofthe first contact arrangement and the second contract arrangement issubstantially the same.
 14. An electric motor or generator according toclaim 12, wherein the second electrical busbar has a first contactarrangement for coupling the first inverter to the capacitor componentand a second contact arrangement for coupling the second inverter to thecapacitor component, wherein the configuration of the first contactarrangement and the second contract arrangement is substantially thesame.
 15. An electric motor or generator according to claim 1, whereinthe first control device includes a first inverter for controllingcurrent flow in the first coil set and the second control deviceincludes a second inverter for controlling current flow in the secondcoil set, wherein each inverter is coupled to the first capacitor,wherein the capacitor component includes a first electrical busbarcoupled to a first electrical terminal of the first capacitor and asecond electrical busbar coupled to a second electrical terminal of thefirst capacitor, wherein the first inverter and second inverter arecoupled to the first electrical busbar and the second electrical busbar.16. An electric motor or generator according to claim 1, wherein eachcoil set includes three coil sub-sets.
 17. An electric motor orgenerator according to claim 1, wherein the capacitor component includesa first capacitor.
 18. An electric motor or generator according to claim1, wherein the capacitor component includes a stack of film sheetshaving a plurality of internal electrodes and dielectric sheetsinterposed between them that form the first capacitor, the secondcapacitor and the third capacitor.
 19. An electric motor or generatoraccording to claim 18, wherein a first and a second outer surface of thecapacitor component that are substantially normal to the plurality ofinternal electrodes are covered by a metallic coating.
 20. An electricmotor or generator according to claim 18, wherein a first and a secondouter surface of the capacitor component that are substantially normalto the plurality of internal electrodes are covered by a metalliccoating, wherein the capacitor component includes a first and a secondelectrically insulating separator film sheet that seperates the stack offilm sheets between the first, the second and the third capacitor, andwherein the first electrically insulating separator film sheet isarranged to seperate the metallic coating on the first outer surfaceinto a first section and a second section that are insulated from eachother, and the second electrically insulating separator film sheet isarranged to seperate the metallic coating on the second outer surfaceinto a first section and a second section that are insulated from eachother.
 21. An electric motor or generator according to claim 1, whereinthe capacitor component includes a first and a second electricallyinsulating separator film sheet that seperates the stack of film sheetsbetween the first, the second and the third capacitor.
 22. An electricmotor or generator according to claim 1, wherein the first busbar andthe second busbar are arranged to electrically couple the first, thesecond and the third capacitor.
 23. An electric motor or generatoraccording to claim 22, wherein the first busbar, the second busbar, thefirst capacitor, the second capacitor and the third capacitor are formedas a ring that enclose a common axis, whereby each of the first busbarand the second busbar have a diameter that is greater than that of thefirst, the second and the third capacitor.
 24. An electric motor orgenerator according to claim 1, wherein the capacitor component includesa first electrical busbar coupled to a first electrical terminal of thefirst capacitor and a second electrical busbar coupled to a secondelectrical terminal of the first capacitor, wherein the capacitorcomponent includes a first and a second electrically insulatingseparator film sheet that seperates the stack of film sheets between thefirst, the second and the third capacitor, and wherein the first busbaris electrically connected to the first section on the first outersurface, and the second busbar is connected to the first section on thesecond outer surface and to the second section on the first outersurface, and in which the second section of the second outer surface isconnected to a reference potential.